The present invention generally relates to the field of image reconstruction in Computed Tomography (CT) imaging systems and more particularly to a system and method for iterative reconstruction of cone beam tomographic images.
CT scanners operate by projecting fan shaped or cone shaped X-ray beams through an object. The X-ray beams are generated by an X-ray source, and are generally collimated prior to passing through the object being scanned. The attenuated beams are then detected by a set of detector elements. The detector element produces a signal based on the intensity of the attenuated X-ray beams, and the signals are processed to produce projections. By using reconstruction techniques, such as filtered backprojection, useful images are formed from these projections.
A computer is able to process and reconstruct images of the portions of the object responsible for the radiation attenuation. As will be appreciated by those skilled in the art, these images are computed by processing a series of angularly displaced projection images. This data is then reconstructed to produce the reconstructed image, which is typically displayed on a cathode ray tube, and may be printed or reproduced on film.
As CT scanners are developed with larger and larger detectors, they begin to encounter problems with artifacts in the reconstructions that arise due to the cone angle of the scanner. An increase in the cone angle beyond a certain limit, can result in a degradation of the image quality produced by the scanner.
One technique that has been employed to address cone beam artifacts is through the use of iterative reconstruction techniques. However, iterative reconstruction techniques require enormous amounts of computation and are not useful in practice unless the volume to be reconstructed is small. A technique for obtaining improved image quality without the high computational burden associated with it is therefore desired.